What is the average number of units sold by Company D over all the years together ........

Quantitative Aptitiude (CLAT) Data Interpretation

Answer the questions based on the information given in the following table. A, B, C, D, E denote companies and 2006, 2007, 2008, 2009, & 2010 denote years.
Number of Units Manufactured (M) and Number of Units Sold (S) (in hundreds) by five different companies over the years.